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DAVID J. MALAN: All right.

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So this is "CS50 Explained, Behind
the Pedagogy," our first session

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of the workshop that's really
meant to give you a sense,

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as teachers or prospective teachers,
a sense of the why we for CS50

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do things the way we do,
for better or for worse.

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Ultimately, the goal of this whole
initiative for the past many years

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has been to really make
available as OpenCourseWare

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curricular materials that
teachers like yourselves

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are welcome to adopt or
adapt in any way you see fit.

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Indeed, typically, what we found
is that if teachers are wanting

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to teach introductory computer science
or programming or AP Computer Science

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principles or any number of
variants thereof, they might,

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in their first year, especially
if new to teaching itself,

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might want to adopt some of the course's
or all of the course's curriculum

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in some way and really serve the
role more of a teaching assistant,

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leaning on us and our videos and
our homework assignments, a.k.a.

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problem sets, while they walk around
focusing their most precious time,

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the human time, on their own students.

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And then, perhaps, as
they get their footing,

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or if you've been
teaching for many years,

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you might instead pursue more of
a model of adapting the course,

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like any good teacher might when
seeing someone else's materials,

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and make it your own and integrate it
into your own classes as you see fit.

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What I thought we'd do, then,
this morning here in Cambridge

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is just give you a sense, then, of
the why behind the course's pedagogy

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and also just give you
a few building blocks

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if you're only somewhat familiar
with CS50 and its offerings,

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or perhaps familiar only from the
perspective of being a student of sorts

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yourself, having taken the class.

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Along the way, please
feel free to interject

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with any questions via the chat
that I or any of my colleagues

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here can answer.

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Or if you'd like to raise
a virtual hand in Zoom,

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we'll do our best to
keep things interactive.

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And then we'll take and leave
time for a good break at the end

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and then resume with our
second session thereafter.

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So a cursory glance at the
history behind this class,

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if only to give you a sense of why
it combines the topics it does-- here

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at Harvard, for the
past many years, there

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was this branch of courses starting
with Engineering Sciences 100, Applied

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Mathematics 110, and then,
finally, Computer Science 150,

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when computer science
finally became a term,

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academically, that
described a whole field.

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But this was an evolution of a
particularly arcane set of classes,

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if you will, particularly
for those who wanted

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to pursue what originally
was called engineering,

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was eventually called applied
mathematics, and now, of course,

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is called computer science.

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But it was fairly technical for the
particularly initiated-- the already

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initiated.

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Then, at Harvard, too,
some years ago, there

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was a different branch
of courses, if you will,

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starting with a well-known
course here on campus

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called Nat Sci 110, Natural Sciences
110, which eventually evolved

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into a course called
Applied Sciences 10,

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and then eventually
Quantitative Reasoning 20.

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And this was more of a path for the
uninitiated, those less comfortable,

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who wanted to know something about
computing and programming, ultimately,

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but didn't necessarily think they
were going to major in the same.

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And then, eventually,
Harvard, as a university,

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rather started to merge
these two tracks in a sense.

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And we had Applied Sciences 11,
Computer Science 11, and now

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what we're here today to talk
about, a course known as CS50.

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And that all began back in 1989,
which was the first year of CS50

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being offered here on campus.

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And it was and is our introduction
to computer science and programming

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but now for majors and nonmajors.

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And that's perhaps
the key characteristic

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in that it does try to serve
both of those audiences.

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And you'll see today and tomorrow via
what curricular means and pedagogical

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means we aspire to do so.

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As it turns out, I myself happened to
be an undergrad here some years ago,

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and in 1996, as a sophomore,
took this same class.

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As I tell students at the
start of our own course,

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I was a government major at the time.

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I had gravitated from the get-go
at college toward the familiar.

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I rather liked history and
constitutional law, especially

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in high school.

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And so I figured, well,
you major in college

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what you seem to like in high school.

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But it wasn't until sophomore year
that I got up the nerve, the courage

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to just put my toes in the water and
to step in on the first class of CS50

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in September of 1996.

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And, long story short, I was hooked.

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As I tell students today
it was the first course,

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and really, the first field where--

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not to sound too cliche--
but homework was fun.

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I had somehow gone 19 years of being
a good student, focusing on my work,

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but not particularly describing
school or homework as fun.

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But when I discovered computer science,
and particularly programming for me

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early on, something clicked.

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And as I tell students, I would
go back to my dorm at, like,

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7:00 PM on a Friday night, which is when
they would officially post the homework

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assignments, and that's how I
would spend my Friday night well

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into Saturday.

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And, for me, that was a sign--

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changed my major to computer science.

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And, ultimately, that's
what motivated now, really,

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a lot of my interest in,
daresay passion for trying

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to create, whether it's
in computer science

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or any other field for
students, that sort of discovery

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and that encouragement to explore
outside one's own comfort zone.

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So fast-forward several years later,
after finishing college and then

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graduate school in 2007.

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I was rather in the right
place at the right time

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and had an opportunity to take the helm
of this same course as its instructor.

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I was meant to fill in for just a
year, after which the course would

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be taught by someone else.

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And somehow or other, that was,
like, coming up on 16 years ago.

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And so this will be version
16 of the course since 2007.

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And nowadays, in healthy times, it's
indeed one of Harvard's largest courses

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here on campus.

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So this is a photograph of one
of the most beautiful spaces here

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on campus, Sanders Theatre, so to
speak, with a whole lot of students back

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in healthy times and me down here
about to talk about computer science.

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And we hope, of course, to return to
that kind of norm this year and beyond.

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But that is to say there's been a
marked increase in interest here,

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and certainly elsewhere in the world,
in computer science and programming.

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And so, really, what
we'll focus on today

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is the support structure
and the pedagogy

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that we've tried to build up over time.

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The course, as I alluded to
earlier, has, since 2007, also

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been freely available as OpenCourseWare
under what's called a Creative Commons

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license by NCSA, which means that anyone
is welcome to use the material as they

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see fit so long as they
attribute it by CS50,

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so as long as it's
for noncommercial use,

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and so long as they, too, share
their materials, be it videos or PDFs

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or adaptations thereof.

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For more details, Carter, if
you wouldn't mind pasting a URL

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like this in the chat.

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Now, in 2012, it's worth noting
that we had an opportunity

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to not just put material out there
in the spirit of OpenCourseWare.

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But 2012 was when this MOOC craze--

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Massive Open Online Courses,
rather-- begun with Coursera,

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then edX, and a few others as well.

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And this was an opportunity for us
now to focus not just, of course,

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on our own campus, on campus
students, but, really, anyone

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online who might like to learn
but learn as actively as possible.

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For many years, we had put our
videos, our PDFs, the assignments,

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and so forth on the internet.

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But if a student on
elsewhere in the world online

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didn't have a Harvard University
login account to connect to some Linux

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or Unix server here on
campus, the onus was on them

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to figure out how to install a
compiler, an interpreter, or a debugger

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on their own Mac or PC-- doable, but not
necessarily doable by many students who

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don't yet have that footing and might
otherwise struggle with "hello, world,"

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let alone just trying to
configure things like your path

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and your terminal window and the like.

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And so we began to focus in
2012, too, on really making

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tooling and software available
for students and teachers

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alike to eliminate a
lot of that complexity

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so that they could focus
truly on the curriculum

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and less so on the mechanics of just
getting requisite software set up.

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And so thus was born what we now
call CS50x, which is essentially

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the OpenCourseWare version of
the class, typically targeted

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at university or older students.

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But it is exactly the same
curriculum technologically

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and curricularly as the
course here on campus.

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Students, of course,
on campus have access

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to additional support structures,
like human teaching assistants or TAs,

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as you might find in
universities typically.

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But otherwise-- curricularly,
technologically-- everything

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is exactly the same.

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And Carter has kindly pasted this,
and Carter, if you don't mind,

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some of our upcoming URLs as well.

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CS50 has generally steered in the
direction of existing online platforms

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for bringing people together.

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And so if you go to
this URL here, you'll

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see any number of CS50's
online communities--

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Facebook and Reddit and Stack
Overflow and Discord and the like--

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where we've rather tried to bring the
course to the students to decrease,

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rather, the transaction
distance, so to speak,

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between them and asking and
answering questions as opposed

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to focusing on walled gardens
or proprietary tools that

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might require the activation
energy to come into the course.

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Rather, we've tried
to bring folks to it.

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And we've also tried to focus, in
recent years since 2012, again,

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not just in putting curricular
materials out there for folks to use,

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but trying to incubate, encourage,
foster, really, in-person communities.

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The real opportunity at hand, whether
with teachers formally in place

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or just students who
want to learn together,

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is to try to bring them
together as humans.

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And Zoom and other
technologies have certainly

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accelerated this trend online.

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But we have also focused, in healthier
times, and hopefully, this coming year

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and beyond, on helping incubate
in-person communities, be it

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at high schools, middle schools,
universities, nonprofits,

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community groups, or the like.

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And so just to paint a picture of some
of your predecessors, if you will,

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or perhaps some of you here,
here is one of our groups

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in healthier times at
Miami-Dade College,

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led by one of our faculty
member friends there.

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And these are students holding proudly
their CS50 certificates, so to speak,

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at term's end.

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Here are some students in
healthier times from London,

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when we held, with University
College London, a so-called CS50

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hackathon that drew
people together to work

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on their code and their final projects.

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Here are some of our students in India
working on something called CS50x

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Puzzle Day-- more on that in a bit--
bringing students together as well.

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Here in Myanmar was a
student who actually

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organized this many of his classmates to
teach CS50 or introductory programming

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more generally to some
of his own classmates.

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Here, after a CS50x Puzzle
Day, are students in Pakistan.

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Here are students after
the same in Egypt.

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Here are some of our students
before the same in Congo

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about to tackle these
printouts of puzzles.

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And here are some of
our friends who have

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been especially in our thoughts in
recent months in Ukraine as well.

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And these are just
some of the communities

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that have been incubated over time.

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But this has, I think, been a
very deliberate charge on our part

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not to just put curricular
materials out there, but,

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again, to try to bring people,
teachers, and students alike

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together in the form of these
more traditional in-person support

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structures.

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You've heard me allude
now to CS50 AP, which

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is a bit of a deliberate misnomer
in that it isn't necessarily

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an AP or advanced placement
version of the course,

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but really an adaptation designed for
high schools and middle schools alike.

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Its release coincided with the
creation of AP Computer Science

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Principles, with which some
of you might be familiar

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here in the US or also abroad.

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And CS50 is one of the
endorsed curriculum

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providers of that same framework.

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But CS50 AP, when we say
it, really just refers

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to a high school or middle
school, a younger audience

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adaptation of the same course that also
happens to satisfy those requirements.

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But it's an offering
typically that is designed

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to be spread over not maybe 12 or
16 weeks in a typical US semester,

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but maybe 32 or 36 weeks over
a typical US school year.

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With that said, at its inception,
CS50 AP here, which has,

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again, the same curricular
materials as CS50x itself.

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Here's an early snapshot
of all of the high schools

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and universities and others that were
working with us at the course's debut.

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00:11:37,110 --> 00:11:39,720
Every circle in red
represents a high school

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00:11:39,720 --> 00:11:41,220
with which we've worked in the past.

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00:11:41,220 --> 00:11:43,110
Every blue represents a university.

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00:11:43,110 --> 00:11:44,820
This now is several years old.

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00:11:44,820 --> 00:11:46,830
But this, too, was an
opportunity for us to try

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to bring people together as well.

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00:11:48,660 --> 00:11:52,960
And I wish you and I were literally
on that same stage right now.

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00:11:52,960 --> 00:11:55,560
This is a photograph of
one of our earliest cohorts

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00:11:55,560 --> 00:11:59,940
of teachers at our very first CS50
educator workshop here at Harvard.

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00:11:59,940 --> 00:12:02,800
Hopefully, health
circumstances permitting,

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00:12:02,800 --> 00:12:06,782
we'll be able to hold this same workshop
both in person and online next year.

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But these are some of our
teachers with whom we got to meet

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00:12:09,240 --> 00:12:13,200
and the original network of teachers
that began via this whole initiative

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00:12:13,200 --> 00:12:13,770
as well.

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00:12:13,770 --> 00:12:16,800
And in healthier times, too, did
we focus on the students as well.

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Margaret, whom you met
earlier, kindly helped

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00:12:18,930 --> 00:12:23,250
us coordinate with a few other teachers
in New York, public and private,

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00:12:23,250 --> 00:12:24,840
a CS50 hackathon.

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00:12:24,840 --> 00:12:28,530
Unlike our university hackathon,
which tends to start at 7:00 PM

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00:12:28,530 --> 00:12:33,100
and end at 7:00 AM the next
day, this was our first 10:00 AM

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00:12:33,100 --> 00:12:36,035
to 2:00 PM CS50 hackathon--
a little more high school

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00:12:36,035 --> 00:12:38,910
and teacher and parent-friendly--
that just brought students together

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00:12:38,910 --> 00:12:42,420
from five different schools in the
area to work on their problem sets,

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00:12:42,420 --> 00:12:48,300
to attend some stand-up workshops and
the like, and generally just have fun

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00:12:48,300 --> 00:12:51,240
learning and asking questions
and solving problems,

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00:12:51,240 --> 00:12:55,120
all within this domain
here of computer science.

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00:12:55,120 --> 00:12:58,720
So at the risk of overwhelming, just
to give you the lay of the land,

265
00:12:58,720 --> 00:13:01,290
but the whole goal of today and
tomorrow is to just give you

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00:13:01,290 --> 00:13:03,430
a sense of what is available to you.

267
00:13:03,430 --> 00:13:06,185
It is not the sort of menu
via which you must choose

268
00:13:06,185 --> 00:13:07,560
a little something of everything.

269
00:13:07,560 --> 00:13:11,220
But just to give you a sense of
what now exists, one of the FAQs

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00:13:11,220 --> 00:13:15,750
we began to receive shortly after the
course launched in 2015, especially

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00:13:15,750 --> 00:13:18,630
in the form of AP for high
schools and middle schools,

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00:13:18,630 --> 00:13:23,100
was, OK, I've taught this course now to
my first-years or sophomores or maybe

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00:13:23,100 --> 00:13:23,880
seniors.

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00:13:23,880 --> 00:13:26,650
What now, at least for
those younger students?

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00:13:26,650 --> 00:13:30,960
And so in recent years have I and
some of our colleagues here at Harvard

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00:13:30,960 --> 00:13:35,430
began focusing on other
curricular offerings as well,

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00:13:35,430 --> 00:13:37,380
all under the CS50 umbrella.

278
00:13:37,380 --> 00:13:40,140
And so while you've had the
whirlwind tour of the history, where

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00:13:40,140 --> 00:13:45,060
CS50 was the course that existed
as of 1989 and ever since, now

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00:13:45,060 --> 00:13:48,600
we use that same moniker with
suffixes to describe other curricular

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00:13:48,600 --> 00:13:52,710
offerings that assume either
as background CS50 itself

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00:13:52,710 --> 00:13:56,740
or assume as a next step CS50 itself.

283
00:13:56,740 --> 00:13:59,940
So here is the current list
of all curricular offerings--

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00:13:59,940 --> 00:14:03,420
CS50x, which, again, is the
online university and adult

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00:14:03,420 --> 00:14:07,107
offering of the same; CS50 AP,
which is that for younger audiences.

286
00:14:07,107 --> 00:14:08,940
But thanks to some of
our amazing colleagues

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00:14:08,940 --> 00:14:13,020
here do we now have CS50AI, which is an
introduction to artificial intelligence

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00:14:13,020 --> 00:14:14,940
with Python specifically.

289
00:14:14,940 --> 00:14:18,750
It's indeed more software-centric
than it is mathematically-oriented.

290
00:14:18,750 --> 00:14:21,810
It introduces students to any
requisite mathematics they need,

291
00:14:21,810 --> 00:14:25,320
but it's not a theory course as
much as it is a software course.

292
00:14:25,320 --> 00:14:29,475
CS50B is computer science for
business professionals, something

293
00:14:29,475 --> 00:14:31,350
for students in management
school or the like

294
00:14:31,350 --> 00:14:35,550
who just are interested not so much in
the lower-level implementation details,

295
00:14:35,550 --> 00:14:38,550
but rather how you can
leverage technology in business

296
00:14:38,550 --> 00:14:40,890
or just make more informed decisions.

297
00:14:40,890 --> 00:14:43,500
CS50G, introduction
to gaming development

298
00:14:43,500 --> 00:14:47,040
that uses a language called Lua that
allows students on their own Macs

299
00:14:47,040 --> 00:14:49,860
or PCs to create their own
two-dimensional, and then, later

300
00:14:49,860 --> 00:14:53,670
in the course via Unity,
three-dimensional games as well.

301
00:14:53,670 --> 00:14:56,310
CS50L for lawyers-- computer science.

302
00:14:56,310 --> 00:14:59,520
This is similar to B but
targeted specifically

303
00:14:59,520 --> 00:15:03,330
at the legally-minded folks out
there, paralegals and the like,

304
00:15:03,330 --> 00:15:05,670
who want to explore the
intersection of computing

305
00:15:05,670 --> 00:15:09,490
with law in particular--
issues of security and privacy,

306
00:15:09,490 --> 00:15:11,100
intellectual property, and the like.

307
00:15:11,100 --> 00:15:13,770
There's a similar backbone
among many of these courses.

308
00:15:13,770 --> 00:15:15,930
But their focus tends, then, to vary.

309
00:15:15,930 --> 00:15:20,880
CS50P, which is hot off the press, so to
speak-- an introduction to Programming

310
00:15:20,880 --> 00:15:22,650
with Python specifically.

311
00:15:22,650 --> 00:15:27,090
We go all the more into detail on the
syntax of Python, the features thereof.

312
00:15:27,090 --> 00:15:33,570
We stop short of any topics that really
are, and daresay belong in CS50, a.k.a.

313
00:15:33,570 --> 00:15:38,860
CS50x or CS50 AP, which is a proper
introduction to computer science.

314
00:15:38,860 --> 00:15:41,250
So while we might take
for granted in CS50P

315
00:15:41,250 --> 00:15:45,220
that there's a function that sorts
for you, it's in the original course,

316
00:15:45,220 --> 00:15:50,280
CS50 itself, that we actually pull
the lid off of sorting and searching

317
00:15:50,280 --> 00:15:52,410
and algorithms and data
structures more generally.

318
00:15:52,410 --> 00:15:55,560
So CS50P is very much
focused on programming itself

319
00:15:55,560 --> 00:15:58,140
and is designed now to
be a course that students

320
00:15:58,140 --> 00:16:02,790
can take before or during
or after CS50 itself,

321
00:16:02,790 --> 00:16:06,750
as either additional material or perhaps
preparatory material for the same.

322
00:16:06,750 --> 00:16:10,230
CS50S, perhaps for your younger
students or less comfortable students,

323
00:16:10,230 --> 00:16:13,740
is an introduction to programming with
Scratch, the graphical language that we

324
00:16:13,740 --> 00:16:15,570
ourselves use in CS50.

325
00:16:15,570 --> 00:16:18,150
And just the first
week of the class, this

326
00:16:18,150 --> 00:16:23,130
is a version of an introductory course
that you might take three weeks, maybe

327
00:16:23,130 --> 00:16:25,710
even six with your
younger or older students,

328
00:16:25,710 --> 00:16:28,500
to go through at a slower
pace but with a higher ceiling

329
00:16:28,500 --> 00:16:31,080
as to what they can then
do with Scratch itself.

330
00:16:31,080 --> 00:16:35,400
CS50T is an introduction to
understanding technology.

331
00:16:35,400 --> 00:16:40,410
So it's similar to CS50B, the business
class, similar to CS50L, law class.

332
00:16:40,410 --> 00:16:43,860
But it focuses more on
consumer-type technologies--

333
00:16:43,860 --> 00:16:47,040
how the internet works, how your
own Mac or PC works-- and uses

334
00:16:47,040 --> 00:16:49,080
some of the shared backbone
but focuses, really,

335
00:16:49,080 --> 00:16:52,740
on folks who aren't necessarily
business or law-centric

336
00:16:52,740 --> 00:16:55,110
but more generally using technology.

337
00:16:55,110 --> 00:16:58,440
And then lastly but not
least is CS50W, a course

338
00:16:58,440 --> 00:17:00,660
on web programming with
Python and JavaScript

339
00:17:00,660 --> 00:17:04,290
that's meant to, like many of
these, pick up where CS50 leaves off

340
00:17:04,290 --> 00:17:08,310
and be a second course, be it for
students in high school or university

341
00:17:08,310 --> 00:17:12,480
or folks in the real world, to dive
in more deeply into web programming

342
00:17:12,480 --> 00:17:17,250
specifically, assuming as prior
knowledge CS50 or some similar course

343
00:17:17,250 --> 00:17:17,970
as well.

344
00:17:17,970 --> 00:17:21,000
Carter, I think, no need to copy
and paste all of these links.

345
00:17:21,000 --> 00:17:23,290
But if you have the
URL of these slides--

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00:17:23,290 --> 00:17:26,310
which, maybe, Carter, it would make
sense to paste the URL of this slide

347
00:17:26,310 --> 00:17:28,318
into the chat-- you're
welcome to click on each

348
00:17:28,318 --> 00:17:30,360
and every one of these
links, which will lead you

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00:17:30,360 --> 00:17:36,210
to the free OpenCourseWare curriculum of
all of these same courses in one place.

350
00:17:36,210 --> 00:17:39,760
And I'll note here that
characterizing all of these classes,

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00:17:39,760 --> 00:17:44,190
but especially the original class, CS50
itself, are really these two themes.

352
00:17:44,190 --> 00:17:47,520
And in fact, after one or two
or three years of teaching,

353
00:17:47,520 --> 00:17:51,587
I began to reflect on what I
was actually doing and why.

354
00:17:51,587 --> 00:17:54,420
I daresay that, first year of the
course, second year of the course,

355
00:17:54,420 --> 00:17:56,913
I was just focused on
keeping my head above water.

356
00:17:56,913 --> 00:17:58,830
And it's only in recent
years that I've really

357
00:17:58,830 --> 00:18:01,483
noticed themes in my own
approaches, for better or for worse,

358
00:18:01,483 --> 00:18:02,400
to teaching the class.

359
00:18:02,400 --> 00:18:06,360
And I daresay two of them are really
this, accessibility and rigor--

360
00:18:06,360 --> 00:18:09,330
sort of lowering the floor,
so to speak, metaphorically,

361
00:18:09,330 --> 00:18:12,450
for students to make it easier for
them, similar in spirit to what

362
00:18:12,450 --> 00:18:16,080
I hope to do back in 1996,
just put a foot in the door

363
00:18:16,080 --> 00:18:19,770
and get some exposure to CS, but
simultaneously preserving what

364
00:18:19,770 --> 00:18:22,710
at least here on campus
has been a historical rigor

365
00:18:22,710 --> 00:18:26,310
so that the returns, so to
speak, of taking this course

366
00:18:26,310 --> 00:18:28,290
are especially high for students.

367
00:18:28,290 --> 00:18:31,860
And it's a particularly immersive, it's
a particularly intensive experience.

368
00:18:31,860 --> 00:18:37,210
But hopefully are the returns all
the more proportional as well.

369
00:18:37,210 --> 00:18:42,660
And so I daresay students taking
this course, CS50, off campus,

370
00:18:42,660 --> 00:18:47,040
be it online or locally
elsewhere or through high school,

371
00:18:47,040 --> 00:18:51,210
where you don't have the constraints,
temporally, of 12 or just 16 weeks,

372
00:18:51,210 --> 00:18:53,860
but you indeed have 32
weeks at your disposal,

373
00:18:53,860 --> 00:18:56,070
maybe even 52 weeks in total--

374
00:18:56,070 --> 00:18:58,870
that, I think, is indeed
the enabling technology.

375
00:18:58,870 --> 00:19:01,080
This isn't a Harvard course per se.

376
00:19:01,080 --> 00:19:04,380
We are just confined by the
traditional model of a semester.

377
00:19:04,380 --> 00:19:08,970
I think, really, the key ingredient for
students of any academic or curricular

378
00:19:08,970 --> 00:19:12,130
background is just to allow
themselves sufficient time.

379
00:19:12,130 --> 00:19:14,280
And so that's a knob that
we generally recommend

380
00:19:14,280 --> 00:19:18,060
folks turn rather than jettisoning
material or making things easier

381
00:19:18,060 --> 00:19:20,910
and chipping away, therefore, at
these primitives, the second one,

382
00:19:20,910 --> 00:19:24,150
of rigor in particular, just
allowing and structuring, perhaps,

383
00:19:24,150 --> 00:19:27,120
your own classes to just give
students more time-- instead

384
00:19:27,120 --> 00:19:29,700
of one week for a given problem
set or homework assignment,

385
00:19:29,700 --> 00:19:32,280
perhaps two or even
three, and as Margaret

386
00:19:32,280 --> 00:19:35,430
might address in her experience,
and our friend Douglas tomorrow

387
00:19:35,430 --> 00:19:37,980
speak to their own experience
with turning these knobs

388
00:19:37,980 --> 00:19:40,320
and adapting the
material as they see fit,

389
00:19:40,320 --> 00:19:43,020
as might be best for their own students.

390
00:19:43,020 --> 00:19:47,130
This, too, was a key curricular design
early on here on campus, at least,

391
00:19:47,130 --> 00:19:52,300
where we had within the same class,
CS50, different tracks, so to speak.

392
00:19:52,300 --> 00:19:55,650
We, like a lot of universities, have
a model where we have weekly lectures.

393
00:19:55,650 --> 00:19:59,130
So I will lecture once a week to
all of the students in the class,

394
00:19:59,130 --> 00:20:01,260
presenting the week's
concepts and really setting

395
00:20:01,260 --> 00:20:02,830
the stage for the week's assignment.

396
00:20:02,830 --> 00:20:04,780
But our teaching assistants,
who are typically

397
00:20:04,780 --> 00:20:09,130
undergraduates themself who've taken
the class and perhaps others in CS,

398
00:20:09,130 --> 00:20:13,060
they then lead sections or
recitations for maybe 12 to 20

399
00:20:13,060 --> 00:20:15,820
or 30 students in total,
generally on campus,

400
00:20:15,820 --> 00:20:19,120
but for our online extension
school students or adults

401
00:20:19,120 --> 00:20:21,820
through continuing
education, via Zoom as well.

402
00:20:21,820 --> 00:20:25,240
But we've typically, on campus, had
different tracks of these sections

403
00:20:25,240 --> 00:20:28,510
or recitations for those more
comfortable, those less comfortable,

404
00:20:28,510 --> 00:20:30,040
and those somewhere in between.

405
00:20:30,040 --> 00:20:32,822
And we just ask students
to categorize themselves

406
00:20:32,822 --> 00:20:34,030
at the start of the semester.

407
00:20:34,030 --> 00:20:36,190
And we tell them,
you're more comfortable

408
00:20:36,190 --> 00:20:38,740
if you've been, in fact,
programming since you were six years

409
00:20:38,740 --> 00:20:41,380
old or the like, but maybe you
don't have a formal background

410
00:20:41,380 --> 00:20:42,430
in CS or programming.

411
00:20:42,430 --> 00:20:46,000
And that's why you're nonetheless
taking a formal introduction thereto.

412
00:20:46,000 --> 00:20:49,720
You're among those less
comfortable if, like me in 1995,

413
00:20:49,720 --> 00:20:51,580
you didn't even consider
taking the class.

414
00:20:51,580 --> 00:20:53,410
Or you have one foot in
the door and the other one

415
00:20:53,410 --> 00:20:55,160
still out the door
because you're not sure

416
00:20:55,160 --> 00:20:57,535
if computer science or
programming is for you.

417
00:20:57,535 --> 00:20:59,410
And if you're not really
sure where you fall,

418
00:20:59,410 --> 00:21:02,000
we assure students that they're
just somewhere in between.

419
00:21:02,000 --> 00:21:06,280
So we have three different tracks
that generally offer students

420
00:21:06,280 --> 00:21:09,610
the same introduction to computer
science but at a different pace.

421
00:21:09,610 --> 00:21:11,890
And the teaching assistant
leading these tracks might

422
00:21:11,890 --> 00:21:15,340
speak to students at a different
level, allow the conversations, perhaps

423
00:21:15,340 --> 00:21:18,963
if more comfortable, to go all the
more down a detailed rabbit hole,

424
00:21:18,963 --> 00:21:21,130
or, at least, pumping the
brakes, perhaps, for those

425
00:21:21,130 --> 00:21:24,640
less comfortable to make sure everyone
is comfortable on the same page.

426
00:21:24,640 --> 00:21:29,810
I'll note, though, that in recent
years, as the course has grown in size

427
00:21:29,810 --> 00:21:32,590
and as the demographics of
our student body have changed,

428
00:21:32,590 --> 00:21:36,350
we were actually motivated this past
year to introduce a fourth track,

429
00:21:36,350 --> 00:21:39,730
if you will, for those
euphemistically least comfortable,

430
00:21:39,730 --> 00:21:44,440
who really need some additional support
not just with taking the class itself,

431
00:21:44,440 --> 00:21:45,940
but perhaps just with college.

432
00:21:45,940 --> 00:21:48,340
Perhaps they didn't have the
strongest high school or middle school

433
00:21:48,340 --> 00:21:48,840
background.

434
00:21:48,840 --> 00:21:51,010
They don't necessarily
have the instincts,

435
00:21:51,010 --> 00:21:53,890
or they didn't have the high
school that trained them

436
00:21:53,890 --> 00:21:56,170
to take advantage of
the online resources

437
00:21:56,170 --> 00:21:58,430
and the professor's
office hours and the like.

438
00:21:58,430 --> 00:22:01,690
And so in this particular
track for our university

439
00:22:01,690 --> 00:22:04,750
students do we also just help
them structure their days,

440
00:22:04,750 --> 00:22:07,450
structure their time so as
to be successful in college,

441
00:22:07,450 --> 00:22:11,350
because CS50 here on campus has
actually gotten younger over the years.

442
00:22:11,350 --> 00:22:14,278
We used to have a plurality of
sophomore, second-year students.

443
00:22:14,278 --> 00:22:17,320
But over the years, students have
started taking the course more and more

444
00:22:17,320 --> 00:22:21,520
as first-years, which means ours
is the first of maybe four classes

445
00:22:21,520 --> 00:22:23,770
they might take ever in college.

446
00:22:23,770 --> 00:22:27,640
And so the onus has come to us to be
all the more supportive of them just

447
00:22:27,640 --> 00:22:30,680
getting their footing on campus.

448
00:22:30,680 --> 00:22:33,850
It's also been important, if
you know CS50's curriculum,

449
00:22:33,850 --> 00:22:37,630
that we introduce, in my mind,
different languages to students.

450
00:22:37,630 --> 00:22:42,400
Back in the day, in 1996, when I
took the class, it was a course in C.

451
00:22:42,400 --> 00:22:44,500
And the vernacular on
campus was, I know how

452
00:22:44,500 --> 00:22:48,310
to program in C because
I took a course in C.

453
00:22:48,310 --> 00:22:52,570
We eventually introduced, though,
other languages into the same course.

454
00:22:52,570 --> 00:22:55,240
And nowadays, we start
with one week of Scratch.

455
00:22:55,240 --> 00:22:57,653
We then have several
weeks of C, which is still

456
00:22:57,653 --> 00:23:00,070
the backbone of the course as
introduction to programming.

457
00:23:00,070 --> 00:23:04,810
And then we have a few weeks of Python,
added to that some SQL and JavaScript

458
00:23:04,810 --> 00:23:07,810
and the requisite HTML and
CSS so that for many students,

459
00:23:07,810 --> 00:23:10,690
CS50 is designed to
be either a foundation

460
00:23:10,690 --> 00:23:14,230
in computer science for further
studies in a traditional way,

461
00:23:14,230 --> 00:23:17,500
but also a terminal class for
about half of our students,

462
00:23:17,500 --> 00:23:20,620
whereby we know a priori
that half of our students

463
00:23:20,620 --> 00:23:23,650
are not going to take another
CS or programming class.

464
00:23:23,650 --> 00:23:26,620
And we want them to have not just
that foundational mental model

465
00:23:26,620 --> 00:23:30,490
for solving problems with technology,
but also the practical skills

466
00:23:30,490 --> 00:23:33,400
to bring back to the arts, the
humanities, the social sciences,

467
00:23:33,400 --> 00:23:37,090
or the like, so as to solve real-world
problems even with just a semester

468
00:23:37,090 --> 00:23:38,740
of computer science under their belt.

469
00:23:38,740 --> 00:23:43,000
And so our goal with these various
languages and the intensity

470
00:23:43,000 --> 00:23:46,660
of the course is so that students exit
the class with a mental model of, I

471
00:23:46,660 --> 00:23:49,870
learned how to program,
period, as opposed to,

472
00:23:49,870 --> 00:23:53,230
back in my day, what would have
been, I learned how to program in C.

473
00:23:53,230 --> 00:23:56,290
To be fair, we focus on
procedural programming.

474
00:23:56,290 --> 00:23:58,540
It's in other courses that
students here at Harvard

475
00:23:58,540 --> 00:24:02,290
tend to learn a bit more object-oriented
programming, functional programming,

476
00:24:02,290 --> 00:24:05,200
although we touch on briefly
some of those topics.

477
00:24:05,200 --> 00:24:08,890
We hint at them when we introduce
languages like Python and JavaScript,

478
00:24:08,890 --> 00:24:12,970
which lend themselves
to some of those chats.

479
00:24:12,970 --> 00:24:15,850
So I thought it might be
fun, or helpful, perhaps,

480
00:24:15,850 --> 00:24:21,100
to share the few vignettes of curricular
content from the course itself.

481
00:24:21,100 --> 00:24:23,980
Some of you might recognize
these scenes or similar.

482
00:24:23,980 --> 00:24:28,150
I took a few screenshots or photos
from our lectures two years ago.

483
00:24:28,150 --> 00:24:31,930
To be fair, I should qualify this
as this was the first year of COVID

484
00:24:31,930 --> 00:24:33,880
in fall of 2020.

485
00:24:33,880 --> 00:24:36,670
Everything here on campus was
shut down, and almost everyone

486
00:24:36,670 --> 00:24:38,950
was, therefore, online, except us.

487
00:24:38,950 --> 00:24:41,680
We had this a wonderful
silver lining opportunity

488
00:24:41,680 --> 00:24:46,390
to collaborate with a theater here on
campus whose staff was otherwise idled.

489
00:24:46,390 --> 00:24:48,430
And so what you're about
to see is admittedly

490
00:24:48,430 --> 00:24:53,600
a grand implementation of visions that
I've had for 15, 20 years as a teacher.

491
00:24:53,600 --> 00:24:57,700
But when it turns out when you have a
prop shop behind you in the theater,

492
00:24:57,700 --> 00:25:00,220
and talented artisans
who can build things out

493
00:25:00,220 --> 00:25:04,480
of wood and electricity and the like,
you'll see some examples of curriculum

494
00:25:04,480 --> 00:25:05,660
that we brought to life.

495
00:25:05,660 --> 00:25:08,260
But every one of these
examples have I done

496
00:25:08,260 --> 00:25:13,060
in yesteryear using a scrap of paper
that I brought with me or a Sharpie

497
00:25:13,060 --> 00:25:14,200
on the board or the like.

498
00:25:14,200 --> 00:25:18,010
There are lower-budget versions of
each of these demonstrations as well.

499
00:25:18,010 --> 00:25:20,230
But the goal, really, of
each of these vignettes

500
00:25:20,230 --> 00:25:23,950
is to paint a picture of why,
in CS50, we, or I personally,

501
00:25:23,950 --> 00:25:28,037
spend so much time teaching something
like linear search, which maybe we

502
00:25:28,037 --> 00:25:30,370
could get away with just a
few minutes of a description,

503
00:25:30,370 --> 00:25:32,960
maybe a drawing on the
board or a few slides.

504
00:25:32,960 --> 00:25:35,560
But instead, we might
spend 15 or 20 minutes

505
00:25:35,560 --> 00:25:38,500
inviting students in healthy
times up to the front of the class

506
00:25:38,500 --> 00:25:41,290
to demonstrate something
with me, bringing in props

507
00:25:41,290 --> 00:25:43,270
and creating all the more visuals.

508
00:25:43,270 --> 00:25:46,030
The goal in my mind,
just as a teacher, is

509
00:25:46,030 --> 00:25:48,310
to not just get through
the course's curriculum

510
00:25:48,310 --> 00:25:52,150
and say the words or the topics that we
want students to learn, but to create

511
00:25:52,150 --> 00:25:55,540
these memorable moments, spending
perhaps an unusual amount of time

512
00:25:55,540 --> 00:25:59,650
to create those things they can latch
on to mentally, even for years, that

513
00:25:59,650 --> 00:26:03,550
help them orient some arcane
topic in the practicality

514
00:26:03,550 --> 00:26:05,140
that it actually offers.

515
00:26:05,140 --> 00:26:07,090
So you might recognize
something like this.

516
00:26:07,090 --> 00:26:12,760
I, at least, have been a fan since 2007
of talking about binary using lights.

517
00:26:12,760 --> 00:26:16,840
Back in the day, I used some desk
lamps that I found from IKEA.

518
00:26:16,840 --> 00:26:18,760
Nowadays, I might have
a few students come up

519
00:26:18,760 --> 00:26:20,560
and turn on the light
bulbs on their phone.

520
00:26:20,560 --> 00:26:22,353
Turns out when you're
in a proper theater,

521
00:26:22,353 --> 00:26:25,270
you might have dozens of light bulbs
right in front of you, literally,

522
00:26:25,270 --> 00:26:26,270
on the stage.

523
00:26:26,270 --> 00:26:28,660
And so here is an opportunity
where I introduced students

524
00:26:28,660 --> 00:26:33,070
each year to the concept of binary, but
really representation of information,

525
00:26:33,070 --> 00:26:37,450
but rather bringing it to life visually
by turning and turning off light bulbs.

526
00:26:37,450 --> 00:26:41,530
A goal I had had for 14 years,
that first year of COVID when

527
00:26:41,530 --> 00:26:45,730
we were in this theater, was to actually
do searching with physical doors,

528
00:26:45,730 --> 00:26:49,900
to be able to walk up to it, open the
door, and look for something behind it.

529
00:26:49,900 --> 00:26:52,000
I didn't really have
access to seven or eight

530
00:26:52,000 --> 00:26:55,000
or more doors in our typical
classroom in healthy times.

531
00:26:55,000 --> 00:26:57,730
But thankfully, what you're
seeing here is seven doors

532
00:26:57,730 --> 00:27:02,500
from seven different plays that had
used doors with their actual sets

533
00:27:02,500 --> 00:27:03,760
back in healthy times.

534
00:27:03,760 --> 00:27:06,070
Our friends kindly got these
all out of the warehouse

535
00:27:06,070 --> 00:27:10,060
and brought to life here me
searching for the number 6.

536
00:27:10,060 --> 00:27:13,257
We went all out-- or, really, our
friends and artists went all out.

537
00:27:13,257 --> 00:27:15,340
And we didn't just put a
number 6 behind the door.

538
00:27:15,340 --> 00:27:18,520
We put a fuzzy number 6
with googly eyes behind it

539
00:27:18,520 --> 00:27:21,160
as well, really, just for fun
and to bring this to life.

540
00:27:21,160 --> 00:27:24,520
Mind you, too, I was the
only one really in the room,

541
00:27:24,520 --> 00:27:27,250
other than colleagues
running our cameras and such.

542
00:27:27,250 --> 00:27:30,640
All of our students were actually,
this particular year, watching online.

543
00:27:30,640 --> 00:27:33,910
But here you see, for instance,
all of the numbers randomly ordered

544
00:27:33,910 --> 00:27:34,870
behind the doors.

545
00:27:34,870 --> 00:27:37,790
Linear search is the best
you can do with this demo.

546
00:27:37,790 --> 00:27:40,480
We then do a subsequent demo
where a colleague secretly

547
00:27:40,480 --> 00:27:43,490
sorts all of the numbers
behind the closed doors.

548
00:27:43,490 --> 00:27:46,420
And then we do it again with
something like binary search.

549
00:27:46,420 --> 00:27:49,720
Now, with this said, I don't
have access to seven doors

550
00:27:49,720 --> 00:27:51,800
anymore in our more
traditional classroom.

551
00:27:51,800 --> 00:27:55,210
And so I sort of revert to just
grabbing something like a whiteboard

552
00:27:55,210 --> 00:27:59,500
and pieces of paper and drawing with
marker or chalk each of the numbers

553
00:27:59,500 --> 00:28:02,770
I have in mind, covering them
with some scotch tape and paper,

554
00:28:02,770 --> 00:28:04,270
and then treating those as the door.

555
00:28:04,270 --> 00:28:08,410
So here, too, is an example of
how, back in the day and now,

556
00:28:08,410 --> 00:28:12,820
do we do things, really, with the
accessories we have on our desks

557
00:28:12,820 --> 00:28:14,000
and in our cabinets.

558
00:28:14,000 --> 00:28:17,260
This is a colleague of mine,
Brian Yu, who teaches, in fact,

559
00:28:17,260 --> 00:28:20,290
the AI class and web class we
mentioned, where he and I were not

560
00:28:20,290 --> 00:28:23,620
allowed to be in the same room
in 2020 while teaching unmasked.

561
00:28:23,620 --> 00:28:27,670
But here are some plastic numbers
that we found here on Amazon

562
00:28:27,670 --> 00:28:31,840
by searching Amazon for "plastic
numbers," just to bring to life now

563
00:28:31,840 --> 00:28:33,490
the actual sorting of numbers.

564
00:28:33,490 --> 00:28:35,830
And so thanks to these
shelves that we found in back

565
00:28:35,830 --> 00:28:39,310
was Brian able to do
something like sorting,

566
00:28:39,310 --> 00:28:42,100
be it with merge sorts or
the like, and actually give

567
00:28:42,100 --> 00:28:45,640
a visual to that as opposed to
just using PowerPoints or the like.

568
00:28:45,640 --> 00:28:48,970
In CS50, we, of course,
use C. And C has,

569
00:28:48,970 --> 00:28:51,640
for better or for worse,
pointers and memory management.

570
00:28:51,640 --> 00:28:55,360
And you and I often talk about
pointers in the context of addresses

571
00:28:55,360 --> 00:28:57,620
or maybe even addresses on mailboxes.

572
00:28:57,620 --> 00:29:01,190
So it turns out when you have a prop
shop, you can actually use mailboxes.

573
00:29:01,190 --> 00:29:05,050
So here, for instance, was a
variable P representing a pointer.

574
00:29:05,050 --> 00:29:07,840
And when I opened up that
mailbox, I found inside of it

575
00:29:07,840 --> 00:29:09,505
the address of some value--

576
00:29:09,505 --> 00:29:11,760
0x123, for instance.

577
00:29:11,760 --> 00:29:16,560
Brian, in the other room, of course,
had the mailbox at address 0x123.

578
00:29:16,560 --> 00:29:21,790
And inside of his mailbox was the
value, once dereferenced, that we found.

579
00:29:21,790 --> 00:29:24,440
So this, I daresay, is
doable on a more modest scale

580
00:29:24,440 --> 00:29:26,940
if you have a local Home Depot
or hardware store or the like

581
00:29:26,940 --> 00:29:28,560
to get some inexpensive mailboxes.

582
00:29:28,560 --> 00:29:31,050
But this, too, was an example
of just something we wanted

583
00:29:31,050 --> 00:29:33,090
to create memorably for students.

584
00:29:33,090 --> 00:29:35,040
We have another example
that he and I tag

585
00:29:35,040 --> 00:29:39,210
team where, when we talk about variables
and something simple like swapping,

586
00:29:39,210 --> 00:29:41,800
we typically invite a student
on stage-- or, in this case,

587
00:29:41,800 --> 00:29:44,250
Brian-- to just swap the
value of two variables.

588
00:29:44,250 --> 00:29:47,310
Those values, in this case, were
represented by two glasses of water

589
00:29:47,310 --> 00:29:50,250
with some food coloring in them
so they'd stand out on camera--

590
00:29:50,250 --> 00:29:51,960
orange and purple in this case.

591
00:29:51,960 --> 00:29:55,155
And then I sort of playfully,
since Brian's in on the joke,

592
00:29:55,155 --> 00:29:56,973
ask him to swap the two values.

593
00:29:56,973 --> 00:29:58,890
And it's not a matter
of swapping the glasses.

594
00:29:58,890 --> 00:30:02,640
I wanted the purple liquid in the
one glass and the orange liquid

595
00:30:02,640 --> 00:30:05,310
in the other, which, of
course, you can't really

596
00:30:05,310 --> 00:30:09,390
do unless you introduce, of course,
a temporary variable, at least

597
00:30:09,390 --> 00:30:13,140
using traditional means and not
something fancy like bitwise operations

598
00:30:13,140 --> 00:30:13,870
or the like.

599
00:30:13,870 --> 00:30:16,230
So here we had just a
way of bringing to life

600
00:30:16,230 --> 00:30:19,500
why students, when they need
to swap values, which becomes

601
00:30:19,500 --> 00:30:22,320
germane quickly when we
start talking about sorting

602
00:30:22,320 --> 00:30:24,870
and moving things around
in array, hopefully

603
00:30:24,870 --> 00:30:27,450
a memorable moment they can latch on to.

604
00:30:27,450 --> 00:30:32,310
We talk later in the semester
about, as well, hashing.

605
00:30:32,310 --> 00:30:36,210
And here, for instance, is me with
some jumbo playing cards, also found

606
00:30:36,210 --> 00:30:40,110
on Amazon as jumbo playing cards so
that they're not this big but this big.

607
00:30:40,110 --> 00:30:42,120
And this is me bucketizing
them, literally,

608
00:30:42,120 --> 00:30:44,970
with four buckets, each with
a suit from a deck of cards,

609
00:30:44,970 --> 00:30:49,500
and me just figuring out how to hash
each card into the diamonds bucket

610
00:30:49,500 --> 00:30:51,640
or the hearts bucket or the like.

611
00:30:51,640 --> 00:30:57,090
So then, I can at least create four
collections of size 13 instead of 52

612
00:30:57,090 --> 00:31:00,690
and then maybe sort each of
those individual buckets.

613
00:31:00,690 --> 00:31:02,700
I have a habit of wearing today--

614
00:31:02,700 --> 00:31:05,700
and really, always-- black
T-shirts or sweaters.

615
00:31:05,700 --> 00:31:08,010
Well, I realized at some
point that this would actually

616
00:31:08,010 --> 00:31:12,728
be kind of a fun way of introducing
stacks and explaining, perhaps,

617
00:31:12,728 --> 00:31:14,520
that the reason I always
seem to wear black

618
00:31:14,520 --> 00:31:18,083
is because my stack of sweaters at
home looks, of course, like this.

619
00:31:18,083 --> 00:31:21,000
And every time I do the wash, I just
put the new sweaters back on top.

620
00:31:21,000 --> 00:31:23,550
And even though I own a
blue and a red sweater,

621
00:31:23,550 --> 00:31:27,300
if you keep pushing onto the top of the
stack but never exhausting the stack,

622
00:31:27,300 --> 00:31:31,200
you're, of course, going to reuse
and redress in the same way.

623
00:31:31,200 --> 00:31:34,410
Back in the day, when I in college
took a course on databases,

624
00:31:34,410 --> 00:31:36,780
this was not done physically
but just verbally.

625
00:31:36,780 --> 00:31:40,590
But it stayed with me nonetheless,
this idea of locking a database,

626
00:31:40,590 --> 00:31:43,380
be it with locks or
nowadays with transactions.

627
00:31:43,380 --> 00:31:46,710
And so it turns out when you have
colleagues who work in a prop shop,

628
00:31:46,710 --> 00:31:49,380
you can just ask them to bring
out the old-school fridge.

629
00:31:49,380 --> 00:31:54,180
And we use this in CS50 to talk about
issues of databases and concurrency

630
00:31:54,180 --> 00:31:57,930
and not wanting to have
two different users see

631
00:31:57,930 --> 00:32:00,030
two different states
of the same variable,

632
00:32:00,030 --> 00:32:01,780
and therefore, make incorrect decisions.

633
00:32:01,780 --> 00:32:05,940
So it turns out, when you have an actual
refrigerator on stage and a padlock,

634
00:32:05,940 --> 00:32:09,420
you can lock the refrigerator,
the metaphor here being,

635
00:32:09,420 --> 00:32:13,020
what happens if I have a refrigerator
in my home and my roommates

636
00:32:13,020 --> 00:32:15,930
and I both, a few minutes
apart, open the fridge

637
00:32:15,930 --> 00:32:19,170
and realize, wait a minute, we're
out of milk, close the fridge,

638
00:32:19,170 --> 00:32:20,580
and then go to the store?

639
00:32:20,580 --> 00:32:23,370
The next roommate then comes
in and makes that same decision

640
00:32:23,370 --> 00:32:27,660
based on a now-misleading state
because my roommate doesn't

641
00:32:27,660 --> 00:32:29,100
know that I've gone to the store.

642
00:32:29,100 --> 00:32:29,940
So what happens?

643
00:32:29,940 --> 00:32:32,490
He too closes the fridge,
goes to some other store.

644
00:32:32,490 --> 00:32:34,380
We don't bump into each
other in this story.

645
00:32:34,380 --> 00:32:35,250
What happens then?

646
00:32:35,250 --> 00:32:38,970
We get back to the apartment, and
boom, we now have two gallons of milk.

647
00:32:38,970 --> 00:32:41,730
And that's not going to last long.

648
00:32:41,730 --> 00:32:43,380
That's going to spoil before long.

649
00:32:43,380 --> 00:32:44,760
And so we've got a problem.

650
00:32:44,760 --> 00:32:47,670
But we would not have
that problem if I instead

651
00:32:47,670 --> 00:32:51,900
locked the refrigerator, much like
you might lock a table or a row

652
00:32:51,900 --> 00:32:52,860
in a database.

653
00:32:52,860 --> 00:32:56,550
And then one last visual here toward
the end of the CS50 semester--

654
00:32:56,550 --> 00:33:00,150
we introduced students to a bit
of JavaScript and a paradigm

655
00:33:00,150 --> 00:33:03,280
like asynchronicity
and callback functions.

656
00:33:03,280 --> 00:33:06,690
And so this is me on an
old-timey phone calling Brian,

657
00:33:06,690 --> 00:33:08,700
asking him, like, what the weather is.

658
00:33:08,700 --> 00:33:10,170
He didn't know when he picked up.

659
00:33:10,170 --> 00:33:13,680
So he hung up the phone, went
outside to check the weather,

660
00:33:13,680 --> 00:33:16,590
and then he called me back
on that old-timey phone.

661
00:33:16,590 --> 00:33:19,320
And I then picked up some number
of seconds or minutes later,

662
00:33:19,320 --> 00:33:23,580
thereby demonstrating, in this case,
the example of a callback function

663
00:33:23,580 --> 00:33:28,660
that's particularly germane again
in the context of JavaScript.

664
00:33:28,660 --> 00:33:32,710
So separate from these
curricular memorable moments

665
00:33:32,710 --> 00:33:36,310
and these demonstrations on stage,
we also do a lot of live coding.

666
00:33:36,310 --> 00:33:38,567
And whether you've taught
or not taught before,

667
00:33:38,567 --> 00:33:40,400
you might have a different
approach to this.

668
00:33:40,400 --> 00:33:42,970
But I daresay it can definitely
be nerve-wracking and perhaps

669
00:33:42,970 --> 00:33:44,360
something, even, to avoid.

670
00:33:44,360 --> 00:33:47,470
And I will say I myself rather
split the difference where I do

671
00:33:47,470 --> 00:33:51,220
think, pedagogically, there's value in
doing live coding as opposed to just

672
00:33:51,220 --> 00:33:53,440
walking through static slides thereof.

673
00:33:53,440 --> 00:33:55,660
I do admittedly think
there's value in screwing

674
00:33:55,660 --> 00:33:58,120
up in front of your roomful
of students, ideally in a way

675
00:33:58,120 --> 00:34:01,210
that you can figure it out within
a few awkward seconds or minutes.

676
00:34:01,210 --> 00:34:03,220
But that, too, of course, has value.

677
00:34:03,220 --> 00:34:07,180
And I do try to generally split the
difference where I, for instance, might

678
00:34:07,180 --> 00:34:08,540
take code like this.

679
00:34:08,540 --> 00:34:11,380
So, for instance, I'll pull up
this URL myself if, Carter, you

680
00:34:11,380 --> 00:34:13,150
wouldn't mind copy and pasting it, too.

681
00:34:13,150 --> 00:34:18,429
This is just an example, for instance,
of what my own approach to week one's

682
00:34:18,429 --> 00:34:20,380
lecture in CS50 might be.

683
00:34:20,380 --> 00:34:24,550
I've got a whole folder here called,
by my own convention, src1, that just

684
00:34:24,550 --> 00:34:26,469
has a whole bunch of demonstrations.

685
00:34:26,469 --> 00:34:28,900
And these demonstrations
are generally named

686
00:34:28,900 --> 00:34:32,380
in a way that describes what it is I
want to demonstrate, not necessarily

687
00:34:32,380 --> 00:34:35,440
conceptually or curricularly,
but functionally,

688
00:34:35,440 --> 00:34:38,739
like, what does this program do just, so
I and a student can find the demo they

689
00:34:38,739 --> 00:34:41,510
vaguely remember later as well.

690
00:34:41,510 --> 00:34:42,670
And I tend to do this.

691
00:34:42,670 --> 00:34:45,070
As you can see from
this calculator example,

692
00:34:45,070 --> 00:34:49,120
I tend to have calculator
0, 1, 2, 3, 4, which

693
00:34:49,120 --> 00:34:51,100
is really a set of five progressions.

694
00:34:51,100 --> 00:34:54,909
And this is really a cue to
myself that, when I live code,

695
00:34:54,909 --> 00:34:57,472
I want to first implement
for my students version 0.

696
00:34:57,472 --> 00:34:59,680
And then we might have a
quick discussion of the same

697
00:34:59,680 --> 00:35:04,120
because version 0 is usually correct
but just not very well implemented.

698
00:35:04,120 --> 00:35:05,210
It might be messy.

699
00:35:05,210 --> 00:35:08,650
It might not decompose
lots of code very well.

700
00:35:08,650 --> 00:35:10,360
There's opportunities for improvement.

701
00:35:10,360 --> 00:35:15,760
And yet by checkpointing myself with,
then, version 1, 2, 3, 4, and onward,

702
00:35:15,760 --> 00:35:19,030
I then sort of redo or
relive code the same.

703
00:35:19,030 --> 00:35:21,880
I do admittedly, behind
the scenes, always

704
00:35:21,880 --> 00:35:24,380
have a very old-school
technology next to me,

705
00:35:24,380 --> 00:35:27,430
including, right now
today, which is paper.

706
00:35:27,430 --> 00:35:31,120
If you're curious, or if this might
be helpful, just one of CS50's tools

707
00:35:31,120 --> 00:35:33,250
is this tool here called Render50.

708
00:35:33,250 --> 00:35:36,640
There's both a command line
version and a web-based version.

709
00:35:36,640 --> 00:35:39,040
And this is just a
program that facilitates

710
00:35:39,040 --> 00:35:44,557
generating landscape-mode,
syntax-highlighted PDFs of source code

711
00:35:44,557 --> 00:35:45,640
you've written in advance.

712
00:35:45,640 --> 00:35:49,720
And to this day, even though I have
all this technology in front of me,

713
00:35:49,720 --> 00:35:52,990
this is my comfort blanket
because I can always

714
00:35:52,990 --> 00:35:55,990
rely on having an answer
for myself or a next step,

715
00:35:55,990 --> 00:35:59,240
even though I do sometimes
diverge from that same script--

716
00:35:59,240 --> 00:36:01,630
so just to give you a
sense of, how I personally

717
00:36:01,630 --> 00:36:04,870
walk the line of doing live
coding but not in a way that

718
00:36:04,870 --> 00:36:09,220
gets me into unrecoverable problems?

719
00:36:09,220 --> 00:36:11,020
And the problem sets
themselves-- this is

720
00:36:11,020 --> 00:36:13,750
our nomenclature for programming
assignments or homework

721
00:36:13,750 --> 00:36:15,640
assignments, a.k.a. problem sets.

722
00:36:15,640 --> 00:36:17,830
And a problem set
literally might mean that.

723
00:36:17,830 --> 00:36:20,290
It might mean, early in
the semester, the problem

724
00:36:20,290 --> 00:36:24,190
set for students has three or
four smaller problems to solve.

725
00:36:24,190 --> 00:36:26,230
Maybe, later in the
course, a problem set

726
00:36:26,230 --> 00:36:28,457
has just one problem for them to solve.

727
00:36:28,457 --> 00:36:30,790
But these are really just our
homework assignments here.

728
00:36:30,790 --> 00:36:33,730
And I thought I'd share just the
process by which I and now some

729
00:36:33,730 --> 00:36:35,950
of my colleagues, among
them Carter and Brian,

730
00:36:35,950 --> 00:36:38,140
go about creating these
homework assignments.

731
00:36:38,140 --> 00:36:45,100
And in my mind, too, I have always tried
to avoid using or creating problems

732
00:36:45,100 --> 00:36:48,460
that you might typically find
at the end of a textbook,

733
00:36:48,460 --> 00:36:51,370
the end of a chapter,
which are fairly mundane,

734
00:36:51,370 --> 00:36:55,060
fairly uninspiring problems that
absolutely have value when it

735
00:36:55,060 --> 00:36:56,800
comes to the mechanics of programming.

736
00:36:56,800 --> 00:36:59,470
Maybe they touch on
some topic specifically.

737
00:36:59,470 --> 00:37:02,710
But in general, our approach
in CS50 and all of our classes

738
00:37:02,710 --> 00:37:07,900
now has been to find some
idea, some application,

739
00:37:07,900 --> 00:37:10,930
some domain that we can
use to inspire the problem

740
00:37:10,930 --> 00:37:14,800
and then use that as a pivot to the
underlying implementation details

741
00:37:14,800 --> 00:37:16,960
that we really do want
students to glean.

742
00:37:16,960 --> 00:37:19,780
So, for instance, I think
the very first problem

743
00:37:19,780 --> 00:37:24,310
set I wrote for CS50 back
in 2007, give or take,

744
00:37:24,310 --> 00:37:26,950
would have been this, a
program we call Mario.

745
00:37:26,950 --> 00:37:29,470
This is not what students
implement for Mario, though.

746
00:37:29,470 --> 00:37:32,740
But this is a screenshot from the
original Nintendo Super Mario Brothers

747
00:37:32,740 --> 00:37:33,460
game.

748
00:37:33,460 --> 00:37:35,530
But I did notice at the time--

749
00:37:35,530 --> 00:37:39,130
well, this is kind of an interesting
pattern, this pyramid-like shape.

750
00:37:39,130 --> 00:37:42,910
And if you're using a language like C
or most languages that generally print

751
00:37:42,910 --> 00:37:45,790
on the terminal window from
top to bottom, left to right,

752
00:37:45,790 --> 00:37:48,310
this is actually maybe
a little nontrivial.

753
00:37:48,310 --> 00:37:51,310
It'd be a lot easier if the pyramid
were this way because then you could

754
00:37:51,310 --> 00:37:53,770
print one brick, then two, then three.

755
00:37:53,770 --> 00:37:57,380
But here you have to somehow
print out all of this empty sky.

756
00:37:57,380 --> 00:38:00,460
So this inspires one of CS50's
first problems that still,

757
00:38:00,460 --> 00:38:04,900
to this day, which is to have students
create, using C and a terminal window

758
00:38:04,900 --> 00:38:07,720
only, none of the colors,
none of the Mario or pipe,

759
00:38:07,720 --> 00:38:12,340
but just pivot from this picture
to implement, using hashtags,

760
00:38:12,340 --> 00:38:15,400
these individual bricks instead.

761
00:38:15,400 --> 00:38:17,890
Later in the class, we happen
to draw some inspiration

762
00:38:17,890 --> 00:38:22,450
from the world of imagery, if
not forensics or steganography,

763
00:38:22,450 --> 00:38:24,200
the art of hiding information.

764
00:38:24,200 --> 00:38:27,820
And if you kind of look at your
Zoom screen just right, perhaps,

765
00:38:27,820 --> 00:38:31,950
or tilt your laptop, you might kind of
see that this isn't all just red noise

766
00:38:31,950 --> 00:38:33,970
with white dots as well.

767
00:38:33,970 --> 00:38:38,100
There's some cyan in here-- some light
blue, essentially-- wherein there's

768
00:38:38,100 --> 00:38:38,910
a secret message.

769
00:38:38,910 --> 00:38:41,790
And so for this problem
set, we have students

770
00:38:41,790 --> 00:38:44,310
inspired by what I
remembered from my childhood

771
00:38:44,310 --> 00:38:47,280
being something that looked
like this in a cereal box

772
00:38:47,280 --> 00:38:50,130
that also came with
those red glasses that

773
00:38:50,130 --> 00:38:53,950
puts red plastic in front of your eyes
that somehow reveals a secret message.

774
00:38:53,950 --> 00:38:56,910
So we have students in
CS50, using C in this case,

775
00:38:56,910 --> 00:38:58,860
implement the equivalent
of a red filter so

776
00:38:58,860 --> 00:39:01,560
that when they put on those
glasses metaphorically,

777
00:39:01,560 --> 00:39:04,410
or run their now-program, they see this.

778
00:39:04,410 --> 00:39:06,750
And if you grew up
playing Clue or Cluedo,

779
00:39:06,750 --> 00:39:10,890
it was Professor Plum in the lounge with
the candlestick this particular year.

780
00:39:10,890 --> 00:39:14,190
But there, too, this is, again, a
problem that, really, like Mario,

781
00:39:14,190 --> 00:39:17,500
is maybe a couple of loops,
iterating from top to bottom,

782
00:39:17,500 --> 00:39:21,030
left to right-- so some basic
mechanics of procedural programming,

783
00:39:21,030 --> 00:39:24,170
but inspired, ideally now, by an
idea that students can latch on to,

784
00:39:24,170 --> 00:39:27,300
or something that just packages
it in a way that inspires.

785
00:39:27,300 --> 00:39:29,520
Most recently, Carter
and I and the team have

786
00:39:29,520 --> 00:39:32,760
been working on a course called CS50P,
this introduction to programming

787
00:39:32,760 --> 00:39:33,930
with Python.

788
00:39:33,930 --> 00:39:36,700
I'm a big fan of Seinfeld,
even though the older I get,

789
00:39:36,700 --> 00:39:40,020
the fewer my same-age students
seem to this particular show.

790
00:39:40,020 --> 00:39:41,682
So we're finding new shows.

791
00:39:41,682 --> 00:39:44,640
But there is this scene here where
Kramer, if you've watched this show,

792
00:39:44,640 --> 00:39:45,660
goes into a bank.

793
00:39:45,660 --> 00:39:47,490
And the bank is having
a promotion where,

794
00:39:47,490 --> 00:39:52,050
if you are not greeted with a hello,
you receive $100 from the bank.

795
00:39:52,050 --> 00:39:55,080
He goes into this bank, and the
teller says something like "hi"

796
00:39:55,080 --> 00:39:55,830
to him instead.

797
00:39:55,830 --> 00:39:57,510
Kramer demands his $100.

798
00:39:57,510 --> 00:40:00,390
But the banker says, "No,
no, I greeted you with hi.

799
00:40:00,390 --> 00:40:01,740
But hi is not hello.

800
00:40:01,740 --> 00:40:03,120
So some hilarity ensues.

801
00:40:03,120 --> 00:40:05,920
And, long story short, it occurred
to us, well, wait a minute.

802
00:40:05,920 --> 00:40:07,878
Why don't we have students
write a program that

803
00:40:07,878 --> 00:40:10,590
prompts the user via standard
input for a greeting.

804
00:40:10,590 --> 00:40:14,055
And if that greeting starts with--

805
00:40:14,055 --> 00:40:17,610
is not a hello, we print
out $100 they're owed.

806
00:40:17,610 --> 00:40:20,670
But if it starts with an H, which
was the eventual compromise,

807
00:40:20,670 --> 00:40:23,370
they should print out $20
instead, like Kramer got.

808
00:40:23,370 --> 00:40:27,180
And if they print out anything else that
doesn't start with an H or isn't hello,

809
00:40:27,180 --> 00:40:29,670
well, they get printed out $0.

810
00:40:29,670 --> 00:40:32,520
So here this is actually
early on in CS50P.

811
00:40:32,520 --> 00:40:35,400
It's really just a prompt to get input.

812
00:40:35,400 --> 00:40:38,790
It's an if-elif-else kind
of construct, and that's it.

813
00:40:38,790 --> 00:40:41,460
But here, too, we try to
package it in a more fun way.

814
00:40:41,460 --> 00:40:45,180
And these URLs, too, will lead you
to the particular specifications.

815
00:40:45,180 --> 00:40:48,917
There's another problem on CamelCase
converting between it and snake case,

816
00:40:48,917 --> 00:40:51,000
so to speak, to help
students realize that there's

817
00:40:51,000 --> 00:40:52,920
different conventions out there.

818
00:40:52,920 --> 00:40:55,800
There's a problem set where we have
students implement a very, very

819
00:40:55,800 --> 00:40:59,160
lightweight version of a
deterministic finite automaton, a DFA,

820
00:40:59,160 --> 00:41:03,180
or, really, just a soda machine that
somehow maintains state with a variable

821
00:41:03,180 --> 00:41:07,860
and keeps track of how much coin a user
has virtually typed in in order to say,

822
00:41:07,860 --> 00:41:10,980
yes, you're now given your Coke.

823
00:41:10,980 --> 00:41:15,227
Drawing inspiration from the
first tweet ever on Twitter,

824
00:41:15,227 --> 00:41:17,310
which was this from Jack
Dorsey-- "just setting up

825
00:41:17,310 --> 00:41:19,600
my twttr," which was
its nickname early on,

826
00:41:19,600 --> 00:41:21,540
you'll notice there's
no vowels in this word.

827
00:41:21,540 --> 00:41:24,330
So here the pivot for us was
prompt the user for input

828
00:41:24,330 --> 00:41:26,260
and strip out all of the values.

829
00:41:26,260 --> 00:41:30,660
So Twitter becomes T-W-T-T-R,
but do this for any word as well.

830
00:41:30,660 --> 00:41:33,180
In Massachusetts, you can
get a so-called vanity plate.

831
00:41:33,180 --> 00:41:35,940
But there's actually almost
an algorithmic definition

832
00:41:35,940 --> 00:41:39,210
of what the rules are for what
letters you can use and numbers

833
00:41:39,210 --> 00:41:40,003
and in what order.

834
00:41:40,003 --> 00:41:42,420
So we have students implement
something that will validate

835
00:41:42,420 --> 00:41:44,580
an actual Massachusetts license plate.

836
00:41:44,580 --> 00:41:48,480
We have students take a look at
something they might see on their car

837
00:41:48,480 --> 00:41:50,640
or their parents' that
has, of course, fractions.

838
00:41:50,640 --> 00:41:54,570
And we use this as an opportunity to
have students type in a fraction using,

839
00:41:54,570 --> 00:41:58,890
in Python, some try and some excepts,
actually parse that fraction,

840
00:41:58,890 --> 00:42:01,500
printing out the equivalent
percentage, or, if it's

841
00:42:01,500 --> 00:42:05,000
close enough to empty or
full, E or F, respectively.

842
00:42:05,000 --> 00:42:06,750
There's a very popular
place down the road

843
00:42:06,750 --> 00:42:09,330
called Felipe's Taqueria here
in Cambridge that we hope,

844
00:42:09,330 --> 00:42:11,700
if students ever visit Boston,
they might visit as well.

845
00:42:11,700 --> 00:42:15,930
But that's a great demonstration for now
grabbing a whole bunch of menu items,

846
00:42:15,930 --> 00:42:18,930
like the burritos and quesadillas and
others that they have on the menu,

847
00:42:18,930 --> 00:42:23,040
and using a Python dictionary to
map those menu items to prices,

848
00:42:23,040 --> 00:42:27,120
giving students an opportunity
now to index into a dictionary,

849
00:42:27,120 --> 00:42:29,100
at least in a more familiar way.

850
00:42:29,100 --> 00:42:31,530
I grew up with this thing
here, Little Professor,

851
00:42:31,530 --> 00:42:36,090
which was a little device that generates
pseudo-randomly mathematical formulas

852
00:42:36,090 --> 00:42:38,280
on the screen, like one plus two.

853
00:42:38,280 --> 00:42:40,830
And the student has
to type in the answer.

854
00:42:40,830 --> 00:42:44,100
But it's therefore sort of an
opportunity to quiz them on math.

855
00:42:44,100 --> 00:42:46,920
So we have students implement
a Python version thereof.

856
00:42:46,920 --> 00:42:49,350
We have this tradition on
campus, and optionally,

857
00:42:49,350 --> 00:42:52,680
online, for students, where
at the end of the course

858
00:42:52,680 --> 00:42:55,080
and be given an "I took CS50" T-shirt.

859
00:42:55,080 --> 00:42:56,622
We tend to have some extras of these.

860
00:42:56,622 --> 00:42:59,288
So if you are teaching your own
class in the coming year, let us

861
00:42:59,288 --> 00:43:02,100
know, and we'll do our best to
oblige with one or more of these.

862
00:43:02,100 --> 00:43:06,300
But we have students implement
their own image generator.

863
00:43:06,300 --> 00:43:08,820
So I can't do it with
the green screen here.

864
00:43:08,820 --> 00:43:13,380
But they have to take as input a
photograph, for instance, of themselves

865
00:43:13,380 --> 00:43:15,930
and then overlay that
T-shirt in a way that

866
00:43:15,930 --> 00:43:19,140
makes it look virtually like
they're wearing, if prematurely,

867
00:43:19,140 --> 00:43:20,910
their "I took CS50" T-shirt.

868
00:43:20,910 --> 00:43:23,100
Any of you who've used
Google Forms, it turns out

869
00:43:23,100 --> 00:43:25,990
if you poke around with
this response validation,

870
00:43:25,990 --> 00:43:30,330
there's a word there called "regular
expression" that most typical users

871
00:43:30,330 --> 00:43:31,780
might not even know what it means.

872
00:43:31,780 --> 00:43:35,160
But we introduce students in
CS50P to regular expressions

873
00:43:35,160 --> 00:43:39,960
to somehow now bring this familiar
Google form UI to students to life,

874
00:43:39,960 --> 00:43:42,870
and, oh, that's what that now
means, and just connecting it

875
00:43:42,870 --> 00:43:44,430
to their own real world.

876
00:43:44,430 --> 00:43:48,150
And then, lastly, we now have
not only CS50 certificates, PDFs,

877
00:43:48,150 --> 00:43:51,120
that we give to students,
proudly congratulating them

878
00:43:51,120 --> 00:43:53,250
on finishing any of CS50's courses.

879
00:43:53,250 --> 00:43:55,260
We now playfully have
a problem set where

880
00:43:55,260 --> 00:44:00,000
they generate, for this assignment,
a PDF of a shirtificate, which

881
00:44:00,000 --> 00:44:03,390
says their own name, virtually,
on the T-shirt here, and then

882
00:44:03,390 --> 00:44:06,240
some other text above
and below, so here, too,

883
00:44:06,240 --> 00:44:09,210
just examples along the way
of some of CS50's classes

884
00:44:09,210 --> 00:44:13,200
wherein we try to bring fundamentals
of procedural programming, still,

885
00:44:13,200 --> 00:44:15,270
but all the more to life.

886
00:44:15,270 --> 00:44:17,520
And the last visuals I thought
I'd share with everyone

887
00:44:17,520 --> 00:44:19,890
here are just now some of the
course's traditions, which

888
00:44:19,890 --> 00:44:23,850
feed into those earlier missions
of accessibility and rigor

889
00:44:23,850 --> 00:44:26,850
but also generating, ultimately,
a community among students,

890
00:44:26,850 --> 00:44:29,022
certainly on campus, but even now off.

891
00:44:29,022 --> 00:44:31,230
And some of you might know
or heard me allude earlier

892
00:44:31,230 --> 00:44:33,030
to what we call CS50 Puzzle Day.

893
00:44:33,030 --> 00:44:36,690
This is an event that we hold here
at Harvard in September of each year

894
00:44:36,690 --> 00:44:41,100
and then online in March or April of
the subsequent year for students online,

895
00:44:41,100 --> 00:44:44,820
wherein we give students a
printed packet of puzzles--

896
00:44:44,820 --> 00:44:47,460
not jigsaw puzzles, but
logic problems of sorts.

897
00:44:47,460 --> 00:44:50,490
We use this in the first week
of CS50 to send the message

898
00:44:50,490 --> 00:44:53,580
that computer science is really
about problem-solving more generally.

899
00:44:53,580 --> 00:44:54,930
It's not about programming.

900
00:44:54,930 --> 00:44:57,330
And we invite students to
invite their own friends,

901
00:44:57,330 --> 00:44:59,640
even if they've never studied
computer science before.

902
00:44:59,640 --> 00:45:01,200
They can use laptops and Google.

903
00:45:01,200 --> 00:45:05,160
But no programming is needed
or expected for this event.

904
00:45:05,160 --> 00:45:07,770
And it draws hundreds of
students here on campus together,

905
00:45:07,770 --> 00:45:10,020
and in our case, thousands
of students online.

906
00:45:10,020 --> 00:45:12,360
But if you follow a
traditional semester where

907
00:45:12,360 --> 00:45:15,522
your classes might start in
August or September, by all means,

908
00:45:15,522 --> 00:45:16,980
reach out to us after the workshop.

909
00:45:16,980 --> 00:45:20,640
We can provide you with the same packet
of puzzles to run the event locally.

910
00:45:20,640 --> 00:45:24,540
Or we'll also do the same on
scale the subsequent spring.

911
00:45:24,540 --> 00:45:27,270
We end our semester
with the CS50 hackathon.

912
00:45:27,270 --> 00:45:30,030
I alluded to this being our
7:00 PM to 7:00 AM event.

913
00:45:30,030 --> 00:45:32,460
But it can be time-shifted
as you see fit, certainly,

914
00:45:32,460 --> 00:45:36,030
when we bring students together just
more socially, more collaboratively,

915
00:45:36,030 --> 00:45:40,020
to work on in CS50 their capstone
project, their final project, which

916
00:45:40,020 --> 00:45:44,130
is an open-ended challenge at the end
of the semester to build most any piece

917
00:45:44,130 --> 00:45:47,535
of software of interest, subject to
the guidance of their teaching fellow

918
00:45:47,535 --> 00:45:49,410
or teaching assistant,
so that they calibrate

919
00:45:49,410 --> 00:45:52,790
their expectations accordingly,
of course, doing this at 7:00 PM

920
00:45:52,790 --> 00:45:53,670
to 7:00 AM.

921
00:45:53,670 --> 00:45:55,470
Not all students make
it through the night.

922
00:45:55,470 --> 00:45:59,082
Among my favorite photos is this
one here around 4:00 or 5:00 AM.

923
00:45:59,082 --> 00:46:01,290
But at least, in our case,
we typically wake students

924
00:46:01,290 --> 00:46:04,480
up at the end of the event
for pancakes as well.

925
00:46:04,480 --> 00:46:07,380
And then, lastly, an event that
we've long held both on campus

926
00:46:07,380 --> 00:46:10,950
and off is a so-called CS50 Fair,
inspired, really, by what I remember

927
00:46:10,950 --> 00:46:12,790
is like a middle-school science fair.

928
00:46:12,790 --> 00:46:15,570
But at this event, we have
students gather in a large space

929
00:46:15,570 --> 00:46:19,020
on campus, bringing their laptops
at sort of bar-height desks

930
00:46:19,020 --> 00:46:22,470
and just presenting to passersby--
students, faculty, and staff

931
00:46:22,470 --> 00:46:26,820
alike-- what it is they created
for that final capstone project.

932
00:46:26,820 --> 00:46:30,000
And we have music and popcorn
and candy in the background.

933
00:46:30,000 --> 00:46:32,650
We typically invite alumni
or friends from industry

934
00:46:32,650 --> 00:46:35,400
to have their own tables and just
chat with students, in our case,

935
00:46:35,400 --> 00:46:39,000
at the university level, about
full-time or summertime jobs or the like

936
00:46:39,000 --> 00:46:41,160
or what computer science
is like in the real world,

937
00:46:41,160 --> 00:46:43,530
but generally try to make
it as much of a social event

938
00:46:43,530 --> 00:46:47,100
as it is academic so that you
get expressions and interactions

939
00:46:47,100 --> 00:46:49,620
like these-- students
not in the class, not

940
00:46:49,620 --> 00:46:53,310
in computer science, showing off or
seeing what their computer science

941
00:46:53,310 --> 00:46:54,600
classmates have had.

942
00:46:54,600 --> 00:46:57,190
This is one of my favorite
candid photos we took years ago,

943
00:46:57,190 --> 00:47:00,060
clearly amazed at what he saw.

944
00:47:00,060 --> 00:47:01,770
But indeed, that there is the goal.

945
00:47:01,770 --> 00:47:05,310
And in our case-- and this is something
we can sometimes help out with if we

946
00:47:05,310 --> 00:47:06,360
have spares--

947
00:47:06,360 --> 00:47:09,210
but offering up at the end of
the semester, as you see here,

948
00:47:09,210 --> 00:47:15,900
the "I took CS50" T-shirts that mark
the end of CS50 students' experience.

949
00:47:15,900 --> 00:47:18,850
And along the way, suffice it to
say we at least here on campus

950
00:47:18,850 --> 00:47:20,370
take a lot of photos and videos.

951
00:47:20,370 --> 00:47:22,200
We navigate through language.

952
00:47:22,200 --> 00:47:25,530
We're happy to share what the requisite
opt-in or opt-out language is.

953
00:47:25,530 --> 00:47:28,960
Particularly in the K-12 level, you
might need parents' blessing as well.

954
00:47:28,960 --> 00:47:32,760
But I would encourage you to consider,
if your circumstances allow, capturing,

955
00:47:32,760 --> 00:47:37,140
if teaching CS50 or anything like
it, as many of these moments,

956
00:47:37,140 --> 00:47:41,050
academic and otherwise, because it
turns out, one, it's a wonderful way

957
00:47:41,050 --> 00:47:43,800
to look back and for your students
to look back on what it is they

958
00:47:43,800 --> 00:47:44,770
did in your class.

959
00:47:44,770 --> 00:47:47,340
But it's also a wonderful
mechanism for recruiting,

960
00:47:47,340 --> 00:47:50,760
in some sense, to open other
students' eyes to what goes on in your

961
00:47:50,760 --> 00:47:54,090
or their friends' classrooms,
bringing to life a fairly arcane

962
00:47:54,090 --> 00:47:57,030
otherwise subject like CSS
in a way that they might not

963
00:47:57,030 --> 00:47:58,860
have realized was possible.

964
00:47:58,860 --> 00:48:01,260
In the coming sessions
today and tomorrow,

965
00:48:01,260 --> 00:48:04,320
you'll see glimpses of some of the
lower-level implementation details.

966
00:48:04,320 --> 00:48:07,800
Carter and [? Rangshin ?]
alluded to this earlier,

967
00:48:07,800 --> 00:48:10,950
a new tool CS50 uses
called VS Code, a.k.a.

968
00:48:10,950 --> 00:48:12,450
Code Spaces in the cloud.

969
00:48:12,450 --> 00:48:15,480
This is a tool that you'll be
welcome to use in your own class,

970
00:48:15,480 --> 00:48:17,020
certainly try out this weekend.

971
00:48:17,020 --> 00:48:19,920
It's freely available thanks to
Microsoft and GitHub nowadays.

972
00:48:19,920 --> 00:48:23,550
You'll see a little something about
how students access this tool now

973
00:48:23,550 --> 00:48:24,510
via the web.

974
00:48:24,510 --> 00:48:27,150
This, though, is consistent
with my very first comment

975
00:48:27,150 --> 00:48:31,180
about really in the course accessible,
not just in a curricular sense,

976
00:48:31,180 --> 00:48:34,360
but also for teachers and students
who might only have Chromebooks

977
00:48:34,360 --> 00:48:37,000
or might have computer labs
but no administrative access.

978
00:48:37,000 --> 00:48:41,590
Everything in CS50 can be done
with just a browser these days.

979
00:48:41,590 --> 00:48:45,100
And you, the teachers, then,
needn't worry about some

980
00:48:45,100 --> 00:48:47,050
of those lower-level details as well.

981
00:48:47,050 --> 00:48:50,020
For those familiar with some
of CS50's prior tools, a.k.a.

982
00:48:50,020 --> 00:48:53,830
CS50 IDE, almost all of those
features now exist in VS Code,

983
00:48:53,830 --> 00:48:55,750
and more are still to be ported.

984
00:48:55,750 --> 00:48:58,600
This is the environment that you'll
soon see that provides students

985
00:48:58,600 --> 00:49:01,870
with a cloud-based programming
environment, terminal window, File

986
00:49:01,870 --> 00:49:03,820
Explorer, code tabs, and all.

987
00:49:03,820 --> 00:49:07,090
This is a built-in debugger that, thanks
to [? Rangshin, ?] is all the easier

988
00:49:07,090 --> 00:49:11,770
to use at the command line so as to
step through, yourself or your students,

989
00:49:11,770 --> 00:49:13,310
code line by line.

990
00:49:13,310 --> 00:49:18,760
This is a VS Code extension that
Brian and now [? Rangshin ?]

991
00:49:18,760 --> 00:49:22,583
have created that allows you to
implement rubber duck debugging

992
00:49:22,583 --> 00:49:23,500
in your own classroom.

993
00:49:23,500 --> 00:49:25,120
We actually have a whole
lot of rubber ducks

994
00:49:25,120 --> 00:49:27,370
that we're happy to send
out as best we can, too.

995
00:49:27,370 --> 00:49:30,110
But barring a physical rubber
duck in your classroom,

996
00:49:30,110 --> 00:49:32,650
you can use a virtual duck
as well, the idea being,

997
00:49:32,650 --> 00:49:35,830
pedagogically, to help students
here any illogic in their thoughts.

998
00:49:35,830 --> 00:49:38,950
And all this, too, if
curious, can be done locally

999
00:49:38,950 --> 00:49:40,720
on students' own Macs or PCs.

1000
00:49:40,720 --> 00:49:43,270
And for us, this is a goal
at the end of the semester.

1001
00:49:43,270 --> 00:49:47,540
We start students with a completely
self-service cloud-based environment,

1002
00:49:47,540 --> 00:49:50,932
but ultimately aspire now to off-board
them at the end of the course

1003
00:49:50,932 --> 00:49:52,640
so that they can then
stand on their own,

1004
00:49:52,640 --> 00:49:55,390
especially if this was the one
and only CS course for them.

1005
00:49:55,390 --> 00:50:00,290
And, ultimately, they can now
do everything locally as well.

1006
00:50:00,290 --> 00:50:03,280
I hope you'll forgive that I'm
just a few minutes after our mark.

1007
00:50:03,280 --> 00:50:05,890
Why don't we officially
end this session here?

1008
00:50:05,890 --> 00:50:08,620
I'm happy to stick around in
the same Zoom for questions.

1009
00:50:08,620 --> 00:50:16,270
But we will officially return at
12:30 PM, which is in 24 minutes

1010
00:50:16,270 --> 00:50:20,200
here, for a session by Margaret
on using the CS50 AP curriculum.

1011
00:50:20,200 --> 00:50:24,560
But, again, it's really also the
CS50 and CS50x curriculum as well.

1012
00:50:24,560 --> 00:50:28,900
So it's targeted not just at K-12, but
really, audiences younger and older

1013
00:50:28,900 --> 00:50:29,650
alike.

1014
00:50:29,650 --> 00:50:31,570
This, though, was "CS50 Explained."

1015
00:50:31,570 --> 00:50:35,080
Feel free to drop off, do
some work, take a break.

1016
00:50:35,080 --> 00:50:38,860
But otherwise, we'll see you
again in 23 minutes here.

1017
00:50:38,860 --> 00:50:41,200
And I'll be happy to take
questions one-on-one now.

1018
00:50:41,200 --> 00:50:43,260
See you in a bit.

1019
00:50:43,260 --> 00:50:44,000